air content in dry castprecast box culverts
 

air content in dry cast/precast box culverts
maybe this reference can serve you
"air-entrainment shall conform to astm c-231 (aashto t-152)"
two percent is marginal to prevent freeze thaw problems. chances are you'll get a bit more from entrapped plus entrained air, but only the entrained air is greatly effective against freeze-thaw deterioration. the reason they are limiting the air content by specification is that they use a lot of vibration to consolidate the "no slump" concrete. the vibration reduces the air content, so they don't want to be in a position of "guaranteeing" more than a couple of percent air.
functionally, you should be able to specify more air (and get it) but they have to choose between "no slump" and reasonable air content. as the air content increases, so does the "flowability" of the concrete, so technically the more air they add, the less likely they will get true "no slump" concrete. they should, however, be able to control their mix to achieve both appropriate air content values and achieve the consolidation and placement control they desire.
concrete111 (visitor)14 may 02 14:46
thanks to both of you for your help!